Compiling method, apparatus, and program

ABSTRACT

Brings response time of a Web server and the like closer to a targeted value. A controller controlling the average response time elapsed between reception by information processing apparatus of a processing request and response of information processing apparatus to the processing request. The controller including: a section for obtaining a response time goal which is a target value of the average response time; a section for calculating a predicted response time which is a predicted value of the average response time at the time point when a predetermined reference period has elapsed from setting an operation mode in the information processing apparatus, the operation mode being any of a plurality of operation modes which provide different throughputs; and a section for setting the operation mode in the information processing apparatus if predicted response time calculated by the predicted response time calculating section is less than goal.

FIELD OF THE INVENTION

The present invention relates to a controller, an information processingsystem, a control method, and a program. In particular, the presentinvention relates to a controller, an information processing system, acontrol method, and a program which control the average response timethat elapses between the reception by the information processingapparatus of a processing request and the response of the informationprocessing apparatus to the processing request.

BACKGROUND ART

In these years attention is being given to power saving techniquesaiming at reducing heat generation in information apparatuses. Thefollowing documents are considered:

-   -   [Non-Patent Document 1) “Intel® Pentium® Processor Enhanced        Intel SpeedStep Technology”, Webpage        URL://support.intel.com/support/processors/mobile/pm/sb/CS007981.htm    -   [Non-Patent Document 2] M. Elnozahy, M. Kistler, and R.        Rajamony, “EnergyConservation Policies for Web Servers”, USITS        2003    -   [Non-Patent Document 3] N. Kandasamy, S. A. Abdelwahed and J. P.        Hayes, “Self-Optimization in Computer Systems via Online        Control: Application to Power Management”, In Proceedings of the        International Conference on Autonomic Computing, 2004    -   [Non-Patent Document 4] “WebSphere® Extended Deployment        Edition”, Whitepaper,WebpageUIRL:        6.ibm.com/jp/software/websphere/ft/was/xd/pdf/whitepaper.pdf

A technique for changing the operating frequency or voltage of centralprocessing units has been used (for example see Non-Patent Document 1).In order to reduce energy consumption in a Web server by using thistechnique, another technique has been proposed that controls theoperating frequency of the Web server on the basis of a 90% responsetime of the Web server (see Non-Patent Document 2).

The term “90% response time” as used in that document refers to the timerequired for a Web server to respond to 90% of the processing requestssent to the Web server. The 90% response time is used as a measure ofhow quickly the Web server can perform processing. According to thetechnique, the 90% response time is measured at regular time intervals.If the measured value is less than a target value, the operatingfrequency is reduced; if the measured value exceeds the target value,the operating frequency is increased. This allows the target to beachieved while preventing excessive power consumption.

A technique that controls the operating frequency of a Web server inaccordance with the number of processing requests to the Web server hasbeen proposed (see Non-Patent Document 3). According to the technique,the trend in recent variations in the incoming rate of processingrequests is determined from the difference between the incoming rate ofprocessing requests previously measured and the incoming rate ofprocessing requests currently measured and a predicted value of thefeature average response time is calculated on the basis of this trend.Then, the lowest operating frequency that can maintain the averageresponse time less than a target value is set. Thus, if variations inthe processing request incoming rate show a given trend, appropriatecontrol can be performed.

The present invention solves the following problems. Because the 90%response time is determined on the basis of response times over a periodbetween a predetermined past time and the present time, there is a timelag between the change of the operating frequency and a change in the90% response time. Therefore, the 90% response time in the techniquedescribed in Non-Patent Document 1 can fluctuate around the targetvalue. The technique described in Non-Patent Document 1 enablesoperating frequency control at very short time intervals by includingthe function of monitoring TCP/IP packets to measure the 90% responsetime and the function of controlling the operating frequency in thekernel of an operating system. Accordingly, the range of fluctuation isrelatively narrow.

However, because it is difficult to identify the types of processingrequests at the level of TCP/IP packets, only one response time goal canbe addressed for all application programs running on a Web server. Thisis unrealistic and it is desirable that a response time goal be set foreach application program. In fact, the technique described in Non-PatentDocument 4 allows a response time goal to be set for each individualapplication program.

To address more than one target values, processing requests must bemonitored at a higher level such as the HTTP. HTTP requests aremonitored in user space. Measurement of the response time and operatingfrequency control in user space use a greater overhead than in kernelspace. Accordingly, if operating frequency control is performed at shorttime intervals, the performance of Web applications would be decreasedsignificantly.

If a response time goal is provided to a workload manager external to aWeb server as in the technique described in Non-Patent Document 4, theoperating frequency of the Web server must be controlled externallythrough a network. Accordingly, further overhead is consumed. Therefore,it is difficult to set time intervals for controlling the operatingfrequency to a small value on the order of several tens of seconds andthe operating frequency must be controlled at longer time intervals.

If the technique described in Non-Patent Document 2 is applied to such asystem without modification, time intervals for measuring the 90%response time will become considerably long. As a result, the 90%response time can fluctuate in limits far away from the target value.This holds true also for the technique described in Non-Patent Document3. If operating frequency control is performed at long time intervals,the average response time can fluctuate.

SUMMARY OF THE INVENTION

Thus, the present invention provides control apparatus, informationprocessing systems, control methods, and programs that can solve theproblems. This is achieved by a combination of features set forth in theindependent claims. The dependent claims define further advantageousspecific embodiments.

In order to solve the problems, the first aspect of the presentinvention provides a controller for controlling the average responsetime that elapses between the reception by an information processingapparatus of a processing request and the response of the informationprocessing apparatus to the processing request, the controllercomprising: a response time goal obtaining section for obtaining aresponse time goal which is a target value of the average response time;a predicted response time calculating section for calculating apredicted response time which is a predicted value of the averageresponse time at the time point when a predetermined reference periodhas elapsed from setting an operation mode in the information processingapparatus, the operation mode being any of a plurality of operationmodes which provide different throughputs; and an operation mode settingsection for setting the operation mode in the information processingapparatus if the predicted response time calculated by the predictedresponse time calculating section is less than the response time goal.Therefore, according to the present invention, the response time of aWeb server and the like can be brought closer to a target value byreduced overhead.

The summary of the invention provided above does not enumerate allessential features of the present invention. Subcombinations of thefeatures also can constitute the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, features, and advantages of the presentinvention will become apparent upon further consideration of thefollowing detailed description of the invention when read in conjunctionwith the drawing figures, in which:

FIG. 1 shows a general configuration of an information processing system10;

FIG. 2 shows functions of a controller 25 as functional blocks;

FIG. 3 is a transition diagram showing how a Web server 30 makestransitions among stable, transient, and unstable states;

FIG. 4 shows an example of a process performed by the controller 25 forsetting a throughput of the information processing system 10;

FIG. 5 shows details of a process performed at S430 in FIG. 4;

FIG. 6 is a conceptual diagram that models changes in the averageresponse time with time by using a first-order-lag element;

FIG. 7 shows an example of control of the average response time;

FIG. 8 shows functions of a controller 25 in a variation of the presentembodiment, as functional units;

FIG. 9 shows an example of a process performed by the controller 25 forsetting a throughput of an information processing system 10; and

FIG. 10 shows an exemplary hardware configuration of an edge server 20according to the present embodiment or a variation thereof.

DESCRIPTION OF SYMBOLS

-   10 . . . Information processing system-   20 . . . Edge server-   25 . . . Controller-   30 . . . Web server-   200 . . . Response time goal obtaining section-   210 . . . Average response time obtaining section-   220 . . . Request count obtaining section-   230 . . . Predicted response time calculating section-   240 . . . Operation mode setting section

DETAILED DESCRIPTION OF THE INVENTION Description of the Invention

The present invention provides control apparatus, information processingsystems, control methods, and programs that can solve the problems. Inorder to solve the problems, the present invention provides a controllerfor controlling the average response time that elapses between thereception by an information processing apparatus of a processing requestand the response of the information processing apparatus to theprocessing request, the controller comprising: a response time goalobtaining section for obtaining a response time goal which is a targetvalue of the average response time; a predicted response timecalculating section for calculating a predicted response time which is apredicted value of the average response time at the time point when apredetermined reference period has elapsed from setting an operationmode in the information processing apparatus, the operation mode beingany of a plurality of operation modes which provide differentthroughputs; and an operation mode setting section for setting theoperation mode in the information processing apparatus if the predictedresponse time calculated by the predicted response time calculatingsection is less than the response time goal. Thus, according to thepresent invention, the response time of a Web server and the like can bebrought closer to a target value by reduced overhead.

While the present invention will be described below with respect toembodiments thereof, the embodiments are not intended to limit thepresent invention, which is defined in the claims, and not all of thecombinations of features described in the embodiments are essential tothe inventive solution.

FIG. 1 shows an overall configuration of an information system 10. Theinformation processing system 10, which may be a Web system provided inan electronic commerce company, responds to a processing request from anexternal source. The information processing system 10 includes a Webserver 30, an example of the information processing apparatus of thepresent invention, and an edge server 20 which controls and manages theWeb server 30.

The edge server 20 transfers a processing request received from anexternal source to the Web server 30. If the information processingsystem 10 has multiple Web servers 30, the edge server 20 may select aWeb server 30 to which the request is to be transferred on the basis ofthe workloads on the individual Web servers 30, and transfer the requestto that Web server 30. The Web server 30 sends a response to theexternal request to the sender of the request.

The edge server 20 has a controller 25 which controls the averageresponse time that elapses between the reception of a processing requestat the Web server 30 and a response to the request. In particular, thecontroller 25 obtains the average response time of the Web server 30from the Web server 30. If the average response time is longer than atarget value, the controller 25 sets an operation mode that provides ahigher throughput in the Web server 30. On the other hand, if theaverage response time is shorter than the target value, the controller25 sets an operation mode that provides a lower throughput in the Webserver 30.

The controller 25 calculates a predicted value of the average responsetime after a predetermined time period elapses from the previous changeof operation mode and sets an operation mode that provides a predictedvalue less than the target value. The purpose of this is to change theaverage response time stably within a range around the target valuewhile preventing the throughput from being changed excessively even ifthe throughput is controlled at relatively long time intervals.

FIG. 2 shows functions of the controller 25 as functional blocks. Thecontroller 25 includes a response time goal obtaining section 200, anaverage response time obtaining section 210, a request count obtainingsection 220, a predicted response time calculating section 230, and anoperation mode setting section 240. The response time goal obtainingsection 200 obtains a response time goal which is the target value ofthe average response time. The average response time obtaining section210 obtains the average response time during a period from apredetermined past time to the current time at predetermined timeintervals (for example 5 minutes) from the Web server 30. The requestcount obtaining section 220 obtains from the Web server 30 thecumulative count of processing requests received by the Web server 30.The request count obtaining section 220 also obtains the count ofprocessing requests received by the Web server 30 per unit of time.

If the average response time is varying stably within a range, theoperation mode setting section 240 sets an operation mode that providesthe response time goal, regardless of the predicted response time. Ifthe response time is varying in one direction beyond the referencerange, the predicted response time calculating section 230 calculates apredicted response time which is a predicted value of the averageresponse time at a time after a predetermined period elapses from thetime at which one of operation modes that provide different throughputsis set in the Web server 30. The operation mode setting section 240 setsthe operation mode in the Web server 30 if the predicted response timecalculated by the section 230 is less than the response time goal. Thisenables the average response time to quickly approach the response timegoal.

FIG. 3 is a state transition diagram showing how a Web server 30 changesamong three states: stable, transient and unstable. The stable state isa state in which the average response time obtained by the averageresponse time obtaining section 210 changes within predeterminedreference limits with time. For example, after the throughput of the Webserver 30 is constant over a sufficiently long period of time, the Webserver makes transition to this state (S310 and S330).

The transient state is a state in which the average response timeobtained by the average response time obtaining section 210 is changingin one direction beyond one of the reference limits with time. Forexample, if the throughput of the Web server 30 is changed lately, theWeb server 30 makes transition to this state (S300).

The unstable state is a state in which the average response timeobtained by the average response time obtaining section 210 is changingbetween a value within the reference limits and a value greater than theupper reference limit or a value less than the lower limit. For example,the Web server 30 often makes transitions to this sate if the responsetime increases even if the throughput is increased lately (S320 andS340).

FIG. 4 shows an example of a process performed by the controller 25 forsetting the throughput of the information processing system 10. Thecontroller 25 performs the process each time a predetermined time periodelapses. First, the average response time obtaining section 210 obtainsfrom the Web server 30 the average respond time over a period between apredetermined past time and the present time (S400). Then the operationmode setting section 240 determines whether or not changes in theaverage response time are within the reference limits (S410). Forexample, each time the average response time is obtained at S400, theoperation mode setting section 240 may record and compare it with thepreviously recorded average response time to determine whether or notchanges are within the reference range.

If the average response time changes within the reference range (forexample 0.1 second) with time (S410: Within reference range), theoperation mode setting section 240 performs a process for the stablestate (420). In particular, the operation mode setting section 240 setsan operation mode in the Web server 30 that reduces the response time ofthe Web server 30 to a value less than a response time goal. Forexample, if the average response time changes in a range of about 1.5seconds and the response time goal is 3 seconds, the operation modesetting section 240 decreases the throughput by a factor of 2 so thatthe response time immediately after the change of the operation modebecomes3 seconds. The Web server 30 makes transition to the transientstate in which the average response time changes in one direction beyondone of the reference range and, after a sufficiently long period of timeelapses, the average response time approaches the response time goal.

If the average response time changes in one direction beyond thereference range with time (S410: changes in one direction), then theoperation mode setting section 240 performs a process for the transientstate (S430). The details of this process will be described later. Ifthe average response time changes between a value and a value greaterthan the upper limit of the reference range or a value less than thelower limit of the reference range with time (S410: Changes in bothdirections), the operation mode setting section 240 performs a processfor the unstable state (S440).

In particular, the operation mode setting section 240 first obtains themaximum value of the average response times obtained over apredetermined past period of time by the average response time obtainingsection 210. If the maximum value is greater than the response timegoal, the operation mode setting section 240 sets an operation mode thatchanges the average response time equal to the maximum value to a valueless than the response time goal. For example, if the maximum value is 4seconds and the response time goal is 3 seconds, the operation modesetting section 240 sets an operation mode in the Web server 30 thatreduces the throughput to 4/3. If the trend in the frequency of incomingprocessing requests does not change, the response time can be reduced tothe response time goal.

FIG. 5 shows details of the process performed at S430 in FIG. 4. Theresponse time goal obtaining section 200 obtains the response time goal(S500). The request count obtaining section 220 obtains from the Webserver 30 the cumulative count of processing requests received by theWeb server 30 (S510). The time at which the process shown in FIG. 5 isperformed is denoted by t_(c) and the obtained cumulative count ofrequests is denoted by n (t_(c)). The request count obtaining section220 calculates, from the cumulative count of requests, the number ofrequests received by the Web server 30 per unit time (S520).

In particular, the request count obtaining section 220 subtracts thepreviously obtained cumulative count of processing requests from thecurrently obtained cumulative count of processing requests. Thedifference value is denoted by n_(prev) (t_(c)). There quest countobtaining section 220 calculates the average of the difference valuedivided by the reference time period (t_(c)−t_(prev)) and the currentlyobtained cumulative count of processing requests divided by the lapsedtime. The average is the number of processing requests received by theWeb server 30 in the unit time. With the number of processing requestsm(t_(c)), this process can be represented by equation (1):

$\begin{matrix}\text{[Formula 1]} & \; \\{\mspace{79mu}{{m\left( t_{c} \right)} = {\frac{{m_{total}\left( t_{c} \right)} + {m_{prev}\left( t_{c} \right)}}{2} = \frac{\frac{n\left( t_{c} \right)}{t_{c}} + \frac{n_{prev}\left( t_{c} \right)}{t_{c} - t_{prev}}}{2}}}} & (1)\end{matrix}$

Then, the predicted response time calculating section 230 and theoperation mode setting section 240 performs the following process foreach of the multiple operation modes that can be set in the Web server30 (S530). The predicted response time calculating section 230 calculatea predicted response time, which is the predicted value of the averageresponse time at a time after the reference period elapsed from the timeat which the current operation mode is set in the Web server 30 (S540).

More specifically, the predicted response time calculating section 230calculates the predicted response time by using a function that modelschanges in the average response time with time ((r_(avg)(t)) by using afirst-order-lag element. This function can be represented by equation(2), wherein the difference between the response time of the Web server30 when the operation mode is set (R_(goal)±) and the average responsetime provided in the previous stable state (r_(avg)(to)) is used as thegain and a value based on the number of processing requests per unittime and the cumulative count of processing requests is used as the timeconstant T.

[Formula  2] $\begin{matrix}{{r_{avg}(t)} = {{\left( {R_{{goal} \pm} - {r_{avg}\left( t_{0} \right)}} \right) \cdot \left( {1 - e^{\frac{t}{T}}} \right)} + {r_{avg}\left( t_{0} \right)}}} & (2)\end{matrix}$

The predicted response time calculating section 230 uses a value thatchanges in inverse proportion to the level of throughput in theoperation mode as the response time (R_(goal)±) that will be providedwhen the operation mode is set in the Web server 30. For example, thepredicted response time calculating section 230 uses the throughput forachieving the response time goal (P_(goal)), the response time goal(R_(goal)), and the throughput in the operation mode (P_(goal)±) toobtain the response time (R_(goal)±) as

$\begin{matrix}\left\lbrack {{Formula}\mspace{14mu} 3} \right\rbrack & \; \\{\mspace{79mu}{R_{{goal} \pm} = {\frac{P_{goal}}{P_{goal} \pm} \cdot R_{goal}}}} & (3)\end{matrix}$

Then the predicted response time calculating section 230 determines thetime constant T of the function (2) that increases the rate of change ofthe average response time in accordance with increase in the number ofprocessing requests per unit time, and decrease the rate of change inaccordance with increase in the cumulative count of processing requests.For example, the time constant T can be calculated by using equation (4)

$\begin{matrix}\text{[Formula 4]} & \; \\{\mspace{79mu}{T = \frac{{n\left( t_{c} \right)} \cdot \left( {R_{{goal}\; \pm} - {r_{avg}\left( t_{0} \right)}} \right)}{{m\left( t_{c} \right)} \cdot \left( {R_{{goal} \pm} - {r_{avg}\left( t_{c} \right)} - {\Delta\; r}} \right)}}} & (4)\end{matrix}$where Δr is a predetermined small quantity.

With reference to FIG. 6, the process for deriving equation (4) will bedescribed. FIG. 6 shows a conceptual diagram which models changes in theaverage response time with time by using a first-order-lag element. Thetime constant T is represented as the time required for the tangent atthe origin of the curve of the first-order-lag element to reach thetarget value as shown in FIG. 6. The time constant can be represented byequation (5)

$\begin{matrix}\text{[Formula 5]} & \; \\{\mspace{79mu}{T = \frac{R_{{goal} \pm} - {r_{avg}\left( t_{0} \right)}}{k}}} & (5)\end{matrix}$where k is the slope of the tangent.

Using the time Δt required for the average response time to increase byΔr, k can be represented by equation (6):

$\begin{matrix}\text{[Formula 6]} & \; \\{\mspace{79mu}{k = \frac{\Delta\; r}{\Delta\; t}}} & (6)\end{matrix}$

Therefore, the time constant T can be obtained by obtaining Δt for aparticular value of Δr (for example 0.01 msec).

The average response time r_(avg) (t_(c)+Δt) at time t_(c)+Δt can berepresented by equation (7):

[Formula 7]r _(avg)(t _(c) +Δt)=r _(avg)(t _(c))+Δr  (7)

Because the average response time r_(avg)(t_(c)) can be represented byequation (8), the average response time r_(avg) (t_(c)+Δt) at timet_(c)+Δt can also be represented by equation (9).

$\begin{matrix}\text{[Formula 8]} & \; \\{\mspace{79mu}{{r_{avg}\left( t_{c} \right)} = {\frac{1}{n\left( t_{c} \right)} \cdot {\sum\limits_{i = 0}^{{n{(t_{c})}} - 1}r_{i}}}}} & (8) \\\text{[Formula 9]} & \; \\{\mspace{79mu}{{r_{avg}\left( {t_{c} + \Delta_{t}} \right)} = {\frac{1}{n\left( {t_{c} + \Delta_{t}} \right)} \cdot {\sum\limits_{i = 0}^{{n{({t_{c} + {\Delta\; t}})}} - 1}r_{i}}}}} & (9)\end{matrix}$

Here, r_(i) is the response time to each processing request. Thecumulative count of processing requests n(t_(c)+Δt) at time t_(c)+Δt canbe approximated by equation (10) with the cumulative count of processingrequest per unit time m (t_(c)).

[Formula 10]n(t _(c) +Δt)=n(t _(c))+m(t _(c))·Δt  (10)

From equations (7), (9), and (10), equation (11) can be derived.

$\begin{matrix}\text{[Formula 11]} & \; \\{{{{r_{avg}\left( t_{c} \right)} + {\Delta\; r}} = {{\frac{1}{{n\left( t_{c} \right)} + {{{m\left( t_{c} \right)} \cdot \Delta}\; t}} \cdot {\sum\limits_{i = 0}^{{n{(t_{c})}} + {{{m{(t_{c})}} \cdot \Delta}\; t} - 1}r_{i}}} = {\frac{1}{{n\left( t_{c} \right)} + {{{m\left( t_{c} \right)} \cdot \Delta}\; t}} \cdot \left( {{\sum\limits_{i = 0}^{{n{(t_{c})}} - 1}r_{i}} + {\sum\limits_{i = {n{(t_{c})}}}^{{n{(t_{c})}} + {{{m{(t_{c})}} \cdot \Delta}\; t} - 1}r_{i}}} \right)}}}\quad} & (11)\end{matrix}$

Because the average value of the response times over the time Δt isR_(goal)±, equation (12) holds.

$\begin{matrix}\text{[Formula 12]} & \; \\{\mspace{79mu}{R_{{goal} \pm} = {\frac{1}{{{m\left( t_{c} \right)} \cdot \Delta}\; t}{\sum\limits_{i = {n{(t_{c})}}}^{{n{(t_{c})}} + {{{m{(t_{c})}} \cdot \Delta}\; t} - 1}r_{1}}}}} & (12)\end{matrix}$

From equations (8), (11), and (12), equation (13) can be derived.

$\begin{matrix}\text{[Formula 13]} & \; \\\left. {{{r_{avg}\left( t_{c} \right)} + {\Delta\; r}} = {{\frac{1}{{n\left( t_{c} \right)} + {{{m\left( t_{c} \right)} \cdot \Delta}\; t}} \cdot \left( {{{n\left( t_{c} \right)} \cdot {r_{avg}\left( t_{c} \right)}} +}\quad \right.}m{\left( t_{c} \right) \cdot \Delta}\;{t \cdot R_{{goal} \pm}}}} \right) & (13)\end{matrix}$

Solving equation (13) for Δt leads equation (14).

$\begin{matrix}\text{[Formula 14]} & \; \\{\mspace{79mu}{{\Delta\; t} = \frac{{{n\left( t_{c} \right)} \cdot \Delta}\; r}{{m\left( t_{c} \right)} \cdot \left( {R_{{goal} \pm} - {r_{avg}\left( t_{c} \right)} - {\Delta\; r}} \right)}}} & (14)\end{matrix}$

From equations (14) and (5), equation (4) can be derived.

Returning to FIG. 5, each time a predicted response time is calculatedby the predicted response time calculating section 230, the operationmode settings section 240 determines whether or not the predictedresponse time exceeds the response time goal (S550). If the predictedresponse time is less than or equal to the response time goal (S550:NO), the operation mode setting section 240 selects the operation modeas a candidate operation mode to set (S560). If the predicted responsetime is greater than the response time goal (S550: YES), then theselection of an operation mode as a candidate operation mode (S560) isskipped. The process is repeated for each operation mode (S570).

Finally, the operation mode setting section 240 selects one of theoperation modes that provide average response times less than theresponse time goal and sets it in the Web server 30 (S580). For example,the operation mode that provides the lowest throughput may be set. Thiscan minimize energy consumption to the extent that the average responsetime is maintained at a value less than the target response for theperiod up to the next time the throughput is controlled.

The throughput herein may be the operating frequency of a centralprocessing unit, for example. If an operation mode that provides a lowerthroughput is set, the operating frequency of the central processingunit decreases compared with an operation mode that provides a higherthroughput. Consequently, the frequency of operations and therefore thepower consumption in the central processing unit as well as the voltageof the central processing unit can be reduced.

The throughput is not limited to the operating frequency of the centralprocessing unit. For example, it may be the number of central processingunits allocated to a Web application program. In that case, the Webserver 30 has multiple central processing units and, if an operationmode that provides a lower throughput is set, the number of centralprocessing units allocated to the Web application program is reducedcompared with an operation mode that provides a higher throughput.Consequently, the efficiency of execution of other programs executed bythe other central processing units can be improved and the computingresources provided by the central processing units can be usedeffectively without waste.

In other examples, the throughput may be the length of a time sliceduring which the Web application program is given computing time of acentral processing unit, or may be the priority given to the Webapplication program as to scheduling of execution threads. In theseexamples, as is the case with the operating frequency, the computingresource provided by the central processing unit can be effectively usedwithout waste, by appropriately controlling the throughput.

FIG. 7 shows an example of controlling the average response time. Part(a) of FIG. 7 shows changes in the average response time and throughputwhen transition is made from a stable state to a transient state. Whenthe operation mode is changed to reduce the throughput, the averageresponse time gradually increases and approaches the response time goalas shown in part (a).

Part (b) shows changes in the average response time and throughput in atransient state. In the transient state, the operation mode thatprovides the lowest possible throughput that does not cause the averageresponse time to exceed the response time goal after the referenceperiod is set. Accordingly, the Web server 30 is placed in the operationmode in which the throughput is low compared with the case shown in (a).As a result, the average response time rapidly increases compared withthe case shown in part (a). Thus, energy consumption can be reducedcompared with the control shown in (a)

In the transient state, the controller 25 obtains the average responsetime and calculates a predicted response time each time the referenceperiod lapses. The predicted response time gradually increases with timeand exceeds the response time goal. Then, the controller 25 sets in theWeb server 30 an operation mode that provides a higher throughput (whichis indicated by the dashed line in (b)). Thus, the average response timeapproaches but does not exceed the response time goal.

As has been described with reference to FIGS. 1 to 7, with theinformation processing system 10 of the present embodiment, each time areference time elapses, a predicted value of the average response timein the next reference period from the change of the operation mode iscalculated and an operation mode that provides a predicted value lessthan the target value is set. This can change the average response timestably within a range around the target value while preventing thethroughput from being changed excessively even the throughput iscontrolled at relatively long time intervals.

Experiments in which the effects of the present embodiment have beeninvestigated has shown that the present invention can reduce energyconsumption in a Web server 30 by 50% or more as compared with caseswhere the Web server 30 is operated at its maximum operating frequencyall the time. It has been also shown that change in the energyconsumption is negligibly small as compared with cases where the Webserver 30 is operated at a known optimum operating frequency. In theexperiments, SPECjAppServer 2002 is used as the benchmark program andthe IR, which is a setting value of the frequency of processingrequests, is set to 40 and 50. The Web server 30 used was a personalcomputer with Pentium®M1.6 GHz (Pentium is a registered trademark), onwhich WebSphere® application server was running (WebSphere is aregistered trademark).

FIG. 8 shows functions of a controller 25 in a variation of the presentembodiment as functional blocks. A Web serve 30 in the variationexecutes a number of application programs and a response time goal ispreset for each of the application programs. That is, a target value ofa response time that elapses between the reception of a processingrequest by an application and a response to the request is predeterminedand a target value of a response time between the reception of aprocessing request by another application program and a response to therequest is predetermined. These target values may be different from eachother.

A response time goal obtaining section 200 obtains a response time goalof each application program. An average response time obtaining section210 obtains an average response time of each application program, whichis the average value of response times over the period during which theWeb serve 30 is executing the application program. A request countobtaining section 220 obtains from the Web server 30 a cumulative numberof processing requests received by the Web server 30 for eachapplication program. If the average response time of any of theapplication programs exceeds its response time goal, a predictedresponse time calculating section 230 selects the application program asa program for which control is to be performed.

The predicted response time calculating section 230 calculates apredicted response time of the application program that will result wheneach of multiple operation modes is set in the Web server 30. If the Webserver 30 is in a transient state, an operation mode setting section 240selects the operation mode that consumes smallest energy from amongoperation modes that provide predicted response times less than theresponse time goal and sets the mode in the Web server 30. Otheroperations of the operation mode settings section 240 are similar tothose of the operation mode setting section 240 shown in FIG. 2 andtherefore the description thereof will be omitted.

FIG. 9 shows an example of a process performed by the controller 25 forsetting a throughput of an information processing system 10 according tothe variation of the present embodiment. The average response timeobtaining section 210 obtains the average response timéof eachapplication program (S800) and the response time goal obtaining section200 obtains the response time goal of each application program (S810).

The predicted response time calculating section 230 determines whetheror not the average response times of all application programs are lessthan their response time goals (S820). If the average response times ofany of the application programs exceed their response time goals (S820:NO), the predicted response time calculating section 230 subtracts theaverage response time from the response time goal of each of theapplication programs that provide average response times exceeding theirresponse time goals (S830). Then the application program in which thedifference calculated is the largest among the application programs isselected as an application program for which control is to be performed.

On the other hand, if the average response times of all of theapplication programs are less than their response time goals (S820:YES), the predicted response time calculating section 230 selects theapplication program in which the difference between the average responsetime and the response time goal is the smallest as an applicationprogram for which control is to be performed (S840).

The controller 25 uses the average response time and response time goalof the selected application program to perform steps S850 to S880. Inparticular, if step S830 is performed, the operation mode is controlledwith reference to the application program in which the differencebetween the average response time and the response time goal is thelargest. If step S840 is performed, the operation mode is controlledwith reference to the application program the average response time ofwhich nearly exceeds its response time goal. In particular, if the Webserver 30 is in a transient state, the predicted response timecalculating section 230 measures the predicted response time of theapplication program of reference that will be provided if each of theoperation modes is set in the Web server 30. The operation mode settingsection 240 sets in the Web server 30 an operation mode that provides apredicted response time less than the response time goal. Steps S850 toS880 are similar to steps S410 to S440 shown in FIG. 4 and therefore thedescription thereof will be omitted.

As has been describe with respect to the variation, the controller 25can reduce the average response time to a value less then the responsetime goal even though it controls the operation modes at relatively longtime intervals and therefore can obtain values such as the averageresponse time of each individual application program. This allows thecontroller 25 to control the Web server 30 according to the averageresponse time and response time goal of each individual applicationprogram.

FIG. 10 shows an exemplary hardware configuration of an edge server 20according to the present embodiment or a variation thereof. The edgeserver 20 includes a CPU peripheral section including a CPU 1000, a RAM1020, and a graphic controller 1075 which are interconnected through ahost controller 1082, an input/output section including a communicationinterface 1030, a hard disk drive 1040, and a CD-ROM drive 1060 whichare connected to the host controller 1082 through the input/outputcontroller 1084, and a legacy input/output section including a ROM 1010,a flexible disk drive 1050, and an input/output chip 1070 which areconnected to the input/output controller 1084.

The host controller 1082 connects the CPU 1000 and the graphiccontroller 1075, which access the RAM 1020 at higher transfer rates,with the RAM 1020. The CPU 1000 operates according to programs stored inthe ROM 1010 and the RAM 1020 to control components of the edge server20. The graphic controller 1075 obtains image data generated by the CPU1000 on a frame buffer provided in the RAM 1020 and causes it to bedisplayed on a display device 1080. Alternatively, the graphiccontroller 1075 may contain a frame buffer for storing image datagenerated by the CPU 1000.

The input/output controller 1084 connects the host controller 1082 withthe communication interface 1030, the hard disk drive 1040, and theCD-ROM drive 1060, which are relatively fast input/output devices. Thecommunication interface 1030 communicates with external devices througha network. The hard disk drive 1040 stores programs and data used by theedge server 20. The CD-ROM drive 1060 reads a program or data from aCD-ROM 1095 and provides it to the input-output chip 1070 through theRAM 1020.

Connected to the input-output controller 1084 are relatively slowinput/output devices such as the flexible disk drive 1050, and theinput/output chip 1070. The ROM 1010 stores a boot program executed bythe CPU 1000 during boot-up of the edge server 20 and programs dependenton the hardware of the edge server 20. The flexible-disk drive 1050reads a program or data from a flexible disk 1090 and provides it to theinput/output chip 1070 through the RAM 1020. The input/output chip 1070connects the flexible disk 1090, and various input/output devicesthrough ports such as a parallel port, serial port, keyboard port, andmouse port, for example.

A program to be provided to the edge server 20 is stored on a recordingmedium such as a flexible disk 1090, a CD-ROM 1095, or an IC card andprovided by a user. The program is read from the recording medium andinstalled in the edge server 20 through the input/output chip 1070and/or input/output controller 1084 and executed. Operations performedby the edge server 20 under the control of the program are the same asthe operations in the edge server 20 described with reference to FIGS. 1and 9 and therefore the description thereof will be omitted.

The programs may be stored in an external storage medium. The storagemedium may be a flexible disk 1090 or a CD-ROM 1095, or an opticalrecording medium such as a DVD and PD, a magneto-optical recordingmedium such as an MD, a tape medium, or a semiconductor memory such asan IC card. Alternatively, a storage device such as a hard disk or a RAMprovided in a server system connected to a private communication networkor the Internet may be used as the recording medium and the program maybe provided from the storage device to the edge server 20 over thenetwork.

While the present invention has been described with respect toembodiments thereof, the technical scope of the present invention is notlimited to that described with the embodiments. It will be apparent tothose skilled in the art that various modifications or improvements canbe made to the embodiment. It will be apparent from the claims thatembodiments to which such modifications and improvements are made alsofall within the scope of the technical scope of the present invention.

Variations described for the present invention can be realized in anycombination desirable for each particular application. Thus particularlimitations, and/or embodiment enhancements described herein, which mayhave particular advantages to a particular application need not be usedfor all applications. Also, not all limitations need be implemented inmethods, systems and/or apparatus including one or more concepts of thepresent invention. Methods may be implemented as signal methodsemploying signals to implement one or more steps. Signals include thoseemanating from the Internet, etc.

The present invention can be realized in hardware, software, or acombination of hardware and software. A visualization tool according tothe present invention can be realized in a centralized fashion in onecomputer system, or in a distributed fashion where different elementsare spread across several interconnected computer systems. Any kind ofcomputer system—or other apparatus adapted for carrying out the methodsand/or functions described herein—is suitable. A typical combination ofhardware and software could be a general purpose computer system with acomputer program that, when being loaded and executed, controls thecomputer system such that it carries out the methods described herein.The present invention can also be embedded in a computer programproduct, which comprises all the features enabling the implementation ofthe methods described herein, and which—when loaded in a computersystem—is able to carry out these methods.

Computer program means or computer program in the present contextinclude any expression, in any language, code or notation, of a set ofinstructions intended to cause a system having an information processingcapability to perform a particular function either directly or afterconversion to another language, code or notation, and/or reproduction ina different material form.

Thus the invention includes an article of manufacture which comprises acomputer usable medium having computer readable program code meansembodied therein for causing a function described above. The computerreadable program code means in the article of manufacture comprisescomputer readable program code means for causing a computer to effectthe steps of a method of this invention. Similarly, the presentinvention may be implemented as a computer program product comprising acomputer usable medium having computer readable program code meansembodied therein for causing a function described above. The computerreadable program code means in the computer program product comprisingcomputer readable program code means for causing a computer to affectone or more functions of this invention. Furthermore, the presentinvention may be implemented as a program storage device readable bymachine, tangibly embodying a program of instructions executable by themachine to perform method steps for causing one or more functions ofthis invention.

It is noted that the foregoing has outlined some of the more pertinentobjects and embodiments of the present invention. This invention may beused for many applications. Thus, although the description is made forparticular arrangements and methods, the intent and concept of theinvention is suitable and applicable to other arrangements andapplications. It will be clear to those skilled in the art thatmodifications to the disclosed embodiments can be effected withoutdeparting from the spirit and scope of the invention. The describedembodiments ought to be construed to be merely illustrative of some ofthe more prominent features and applications of the invention. Otherbeneficial results can be realized by applying the disclosed inventionin a different manner or modifying the invention in ways known to thosefamiliar with the art.

1. A controller for controlling an average response time that elapsesbetween reception by an information processing apparatus of a processingrequest and a response of information processing apparatus to theprocessing request, the controller comprising: a response time goalobtaining section for obtaining a response time goal which is a targetvalue of the average response time; a predicted response timecalculating section for calculating the predicted response time which isa predicted value of the average response time at a time point when apredetermined reference period has elapsed from setting an operationmode in the information processing apparatus, the operation mode beingany of a plurality of operation modes which provide differentthroughputs; and an operation mode setting section for setting theoperation mode in the information processing apparatus if the predictedresponse time calculated by the predicted response time calculatingsection is less than the response time goal.
 2. The controller accordingto claim 1, further comprising an average response time obtainingsection for obtaining the average response time from the informationprocessing apparatus each time the reference period elapses; wherein, ifthe information processing apparatus is in a transient state in whichthe average response time obtained by the average response timeobtaining section changes in one direction beyond a predeterminedreference range with time; the predicted response time calculatingsection calculates the predicted response time which is provided if eachof the operation modes is set, each time the reference time elapses; andthe operation mode setting section selects any of the operation modesthat provide a predicted response time less than the response time goaland sets the operation mode in the information processing apparatus,each time the predicted response time in each operation mode iscalculated by the predicted response time calculating section; wherein,if the information processing apparatus is in a stable state in whichthe average response time obtained by the average response timeobtaining section changes within the reference range with time, theoperation mode setting section sets an operation mode that changes theresponse time of the information processing apparatus to a value lessthan the response time goal to place the information processingapparatus in the transient state; wherein if the information processingapparatus is in an unstable state in which the average response timeobtained by the average response time obtaining section is changingbetween a value and a value greater than the upper limit of thereference range or a value less than the lower limit of the referencerange with time, the operation mode setting section obtains the maximumvalue of the average response times obtained by the average responsetime obtaining section over a predetermine past period of time and setsin the information processing apparatus an operation mode that reducesthe response time equal to the maximum value to a value less than theresponse time goal; further comprising a request count obtaining sectionfor obtaining the number of processing requests received by theinformation processing apparatus per unit time and the cumulative numberof processing requests received by the information processing apparatus;and wherein the predicted response time calculating section calculatesfor each of the plurality of operation modes the predicted response timeby using a function which models changes in the average response time ofthe information processing apparatus with time by using afirst-order-lag element, wherein the function uses as a gain thedifference between the response time that is provided when the operationmode is set in the information processing apparatus and the averageresponse time in the stable state and uses as a time constant a valuebased on the number of processing requests per unit time and thecumulative number of processing requests.
 3. The controller according toclaim 1, further comprising an average response time obtaining sectionfor obtaining the average response time from the information processingapparatus each time the reference period elapses; wherein, if theinformation processing apparatus is in a transient state in which theaverage response time obtained by the average response time obtainingsection changes in one direction beyond a predetermined reference rangewith time; the predicted response time calculating section calculatesthe predicted response time which is provided if each of the operationmodes is set, each time the reference time elapses; and the operationmode setting section selects any of the operation modes that provide apredicted response time less than the response time goal and sets theoperation mode in the information processing apparatus, each time thepredicted response time in each operation mode is calculated by thepredicted response time calculating section.
 4. The controller accordingto claim 3, wherein, if the information processing apparatus is in astable state in which the average response time obtained by the averageresponse time obtaining section changes within the reference range withtime, the operation mode setting section sets an operation mode thatchanges the response time of the information processing apparatus to avalue less than the response time goal to place the informationprocessing apparatus in the transient state.
 5. The controller accordingto claim 4, wherein if the information processing apparatus is in anunstable state in which the average response time obtained by theaverage response time obtaining section is changing between a value anda value greater than the upper limit of the reference range or a valueless than the lower limit of the reference range with time, theoperation mode setting section obtains the maximum value of the averageresponse times obtained by the average response time obtaining sectionover a predetermine past period of time and sets in the informationprocessing apparatus an operation mode that reduces the response timeequal to the maximum value to a value less than the response time goal.6. The controller according to claim 4, further comprising a requestcount obtaining section for obtaining the number of processing requestsreceived by the information processing apparatus per unit time and thecumulative number of processing requests received by the informationprocessing apparatus; wherein: the predicted response time calculatingsection calculates for each of the plurality of operation modes thepredicted response time by using a function which models changes in theaverage response time of the information processing apparatus with timeby using a first-order-lag element, wherein the function uses as a gainthe difference between the response time that is provided when theoperation mode is set in the information processing apparatus and theaverage response time in the stable state and uses as a time constant avalue based on the number of processing requests per unit time and thecumulative number of processing requests.
 7. The controller according toclaim 6, wherein the predicted response time calculating sectioncalculates for each of the plurality of the operation modes thepredicted response time by using a value inversely proportional to thethroughput in the operation mode as a response time that is provided ifthe operation mode is set in the information processing apparatus. 8.The controller according to claim 6, wherein the predicted response timecalculating section calculate the predicted response time by increasingthe rate of change in accordance with increase in the number ofprocessing requests per unit time and decreasing the rate of change inaccordance with increase in the cumulative number of processingrequests.
 9. The controller according to claim 6, wherein the requestcount obtaining section obtains from the information processingapparatus the cumulative number of processing requests received by theinformation processing apparatus, each time the reference periodelapses, subtracts the previously obtained cumulative number ofprocessing requests from the currently obtained cumulative number ofprocessing requests to obtain the difference, and obtains the average ofthe difference divided by the reference period and the currentlyobtained cumulative number of processing requests divided by thecumulative elapsed time as the number of processing requests received bythe information processing apparatus per unit time.
 10. An informationprocessing system, comprising: the information processing apparatusresponding to a processing request received from an external source; anda controller for controlling the average response time that elapsesbetween the reception by the information processing apparatus of aprocessing request and the response of the information processingapparatus to the processing request; the controller having; a responsetime goal obtaining section for obtaining a response time goal which isa target value of the average response time; a predicted response timecalculating section for calculating a predicted response time which is apredicted value of the average response time at the time point when apredetermined reference period has elapsed from setting an operationmode in the information processing apparatus, the operation mode beingany of a plurality of operation modes which provide differentthroughputs; and an operation mode setting section for setting theoperation mode in the information processing apparatus if the predictedresponse time calculated by the predicted response time calculatingsection is less than the response time goal.
 11. The informationprocessing system according to claim 10, wherein the informationprocessing apparatus executes each of a plurality of applicationprograms; the response time goal obtaining section obtains the responsetime goal of each of the application programs; the informationprocessing system farther comprises an average response time obtainingsection for obtaining for each of the application program the average ofresponse times over a period during which the information processingapparatus is executing the application program as the average responsetime; and if the average response time of any of the applicationprograms exceeds the response time goal, the predicted response timecalculating section calculates the predicted response time that isprovided if any of the plurality of operation modes is set for theapplication program; and if the predicted response time calculated bythe predicted response time calculating section is less than theresponse time goal, the operation mode setting section sets theoperation mode in the information processing apparatus; wherein: if theaverage response time of any of the plurality of application programsexceeds the response time goal, the predicted response time calculatingsection selects the application program in which the difference betweenthe average response time and the response time goal is the largestamong the plurality of application programs and calculates a predictedresponse time of the application program that is provided if theoperation mode is set in the information processing apparatus; and theoperation mode setting section sets the operation mode in theinformation processing apparatus if the predicted response timecalculated by the predicted response time calculating section is lessthan the response time goal of the application program wherein: if theaverage response times of all of the application programs are less thanthe response time goals, the predicted response time calculating sectionselects the application program in which the difference between theaverage response time and the response time goal is the smallest amongthe application programs, and calculates a predicted response time ofthe application program that is provided if the operation mode is set inthe information processing apparatus; and the operation mode settingsection sets the operation mode in the information processing apparatusif the predicted response time calculated by the predicted response timecalculating section is less than the response time goal of theapplication program.
 12. The information processing system according toclaim 10, wherein the information processing apparatus executes each ofa plurality of application programs; the response time goal obtainingsection obtains the response time goal of each of the applicationprograms; the information processing system further comprises an averageresponse time obtaining section for obtaining for each of theapplication program the average of response times over a period duringwhich the information processing apparatus is executing the applicationprogram as the average response time; and if the average response timeof any of the application programs exceeds the response time goal, thepredicted response time calculating section calculates the predictedresponse time that is provided if any of the plurality of operationmodes is set for the application program; and if the predicted responsetime calculated by the predicted response time calculating section isless than the response time goal, the operation mode setting sectionsets the operation mode in the information processing apparatus.
 13. Theinformation processing system according to claim 12, wherein: if theaverage response time of any of the plurality of application programsexceeds the response time goal, the predicted response time calculatingsection selects the application program in which the difference betweenthe average response time and the response time goal is the largestamong the plurality of application programs and calculates a predictedresponse time of the application program that is provided if theoperation mode is set in the information processing apparatus; and theoperation mode setting section sets the operation mode in theinformation processing apparatus if the predicted response timecalculated by the predicted response time calculating section is lessthan the response time goal of the application program.
 14. Theinformation processing system according to claim 12, wherein: if theaverage response times of all of the application programs are less thanthe response time goals, the predicted response time calculating sectionselects the application program in which the difference between theaverage response time and the response time goal is the smallest amongthe application programs, and calculates a predicted response time ofthe application program that is provided if the operation mode is set inthe information processing apparatus; and the operation mode settingsection sets the operation mode in the information processing apparatusif the predicted response time calculated by the predicted response timecalculating section is less than the response time goal of theapplication program.
 15. A control method for controlling an averageresponse time that elapses between reception by an informationprocessing apparatus of a processing request and a response ofinformation processing apparatus to the processing request; the controlmethod comprising: a response time goal obtaining step of obtaining aresponse time goal which is a target value of the average response time;a predicted response time calculating step of calculating a predictedresponse time which is a predicted value of the average response time atthe time point when a predetermined reference period has elapsed fromsetting an operation mode in the information processing apparatus, theoperation mode being any of a plurality of operation modes which providedifferent throughputs; and an operation mode setting step of setting theoperation mode in the information processing apparatus if the predictedresponse time calculated by the predicted response time calculatingsection is less than the response time goal.